The present invention is based on an actuator.
Conventionally, actuators for operation of fuel injectors in fuel injection systems of internal combustion engines are prestressed by a spring to prevent tensile stress. This spring prestress is generally produced by using the residual tension in the restoring spring of the valve even when the fuel injector is closed. Such an arrangement is described in German Patent No. 195 34 445, for example. The actuator sits on an abutment which is pressed against a pressure shoulder by the restoring spring.
One disadvantage of this design is that the spring prestress of the actuator cannot be preset. This results in damage to the component before or during installation. Since this actuator is not monolithic, but instead is composed of multiple piezoelectric or magnetostrictive ceramic layers, it is very sensitive to shearing forces, which can lead to very rapid destruction of the component.
An actuator according to one example embodiment of the present invention has the advantage that by using a prestressing device, a variable actuator prestress is possible, the prestress being applied at the time of manufacture of the actuator, so the actuator is also not exposed to any tensile stress during assembly.
It is advantageous to install the actuator in the fuel injector in such a way that it is prestressed, because this prevents damage to the component.
Furthermore, the prestressing device can be implemented with a low manufacturing expense and practically no additional installation space.
Using a central tie rod for the prestressing device also offers the advantage that the prestressing device can be accommodated in a central recess in the actuator in a space-saving manner. This example embodiment protects the actuator from destruction due to shearing forces and allows prestressed installation of the actuator. The prestressing device can be implemented in a technically simple and inexpensive manner.
Using a flanged sheathing for the prestressing device also has the advantage of a space-saving design, but it offers better protection against forces acting during installation of the component due to the sheathing on the actuator. The flanging on the sheathing can be implemented easily and inexpensively.